This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for DYNAMIC FOCUS REGULATION CIRCUIT FOR DISPLAY DEVICE earlier filed in the Korean Industrial Property Office on Aug. 31, 2001 and there duly assigned Serial No. 2001-53306.
1. Field of the Invention
The present invention relates in general to a display apparatus, and more particularly, to a dynamic focus regulation circuit for supplying a uniform parabolic waveform voltage regardless of variation of a horizontal frequency in a display mode.
2. Description of the Related Art
In a CRT (cathode ray tube) of a display apparatus, an electron beam is emitted from an electron gun unit to a panel coated with red/green/blue fluorescent material so as to form pixels, and thus a 2-dimensional picture is displayed on the panel by supplying a saw tooth waveform electric current to vertical and horizontal deflection coils.
In the conventional CRT, the panel is curved outwardly, and the distance between the electron gun unit and the panel is not uniform, and thus the sharpness of the picture becomes different according to the positions of pixels. That is, the sharpness on the edge of the panel is inferior to that on the center thereof. In the case of a high-resolution monitor, the above phenomenon is regulated by applying a regulation waveform voltage to the CRT focus voltage component by a focus regulation circuit. The regulation waveform is induced by an H-DY (Horizontal Deflection Yoke) generally outputting a horizontal deflection signal, and is synchronized with a deflection signal having a parabolic waveform.
FIG. 5 illustrates a conventional dynamic focus regulation circuit detecting a dynamic focus output waveform. As shown therein, the dynamic focus regulation circuit comprises a horizontal deflection circuit 110 oscillating a horizontal deflection signal, an S-regulation circuit 120 regulating an electric current outputted from the horizontal deflection circuit 110, a dynamic focus output circuit 130 outputting a dynamic focus waveform voltage by amplifying the parabolic waveform voltage from the S-regulation circuit 120, and a diode modulation circuit 140 horizontally modulating a raster.
The horizontal deflection circuit 110 includes a horizontal driving transistor 112, a damper diode 114, a resonance capacitor 116, and an H-DY 118.
The horizontal driving transistor 112 is switched on/off according to a horizontal driving signal generated by a video IC (not shown) or a horizontal oscillating IC (not shown). When the horizontal driving transistor 112 is switched on, B+ electric power from an FBT (Fly Back Transformer) is supplied to the H-DY 118.
If the horizontal driving transistor 112 is rapidly switched on according to the horizontal driving signal, an electric current is induced to the H-DY 118. On the other hand, if the horizontal driving transistor 112 is switched off, the electricity stored in the H-DY 118 is charged in the resonance capacitor 116. Herein, when the resonance capacitor 116 is perfectly charged with the electricity, the resonance capacitor 116 discharges its electricity to the H-DY 118, thereby re-storing the H-DY 118 with the electricity. Thereafter, according as the H-DY 118 is stored with electric energy, when the voltage of the H-DY 118 is so high that a forward bias can be applied to the damper diode 114, the damper diode 114 is shorted and the electricity of the H-DY 118 vanishes.
Thus, when the electricity of the H-DY 118 vanishes into zero, the horizontal driving transistor 112 is switched on again by the horizontal driving signal, to thereby repeat the above described process. Thus, an electric current having a saw tooth waveform is generated for deflecting an electron beam horizontally.
The S-regulation circuit 120 regulates the saw tooth waveform electric current applied to the H-DY 118 so as to maintain the linearity of a screen. The S-regulation circuit 120 includes a basic S-regulation capacitor 119 connected with the H-DY 118 and the resonance capacitor 116 in parallel, an S-regulation capacitor 122, and a switching transistor 124 switching on/off the S-regulation capacitor 122. Herein, the switching transistor 124 is controlled by a microcomputer 150.
With this configuration, if electric power is supplied to the S-regulation capacitor 122 by switching on/off the switching transistor 124 according to control of the microcomputer 150, the voltage applied to the H-DY 118 is regulated by means of combination of the capacitance of the S-regulation capacitor 122 and the capacitance of the basic S-regulation capacitor 119, thereby regulating the chopping waveform electric current.
Further, the dynamic focus output circuit 130 inverting-amplifies the convex parabolic waveform voltage across opposite ends of the basic S-regulation capacitor 119, to thereby output the dynamic focus waveform voltage.
The dynamic focus output circuit 130 is connected with two ends of the basic S-regulation capacitor 119, and includes a capacitor 134 applying only the AC signal of the convex parabolic waveform voltage through DC-coupling, a transformer (T) 132 inverting-boosts the convex parabolic waveform voltage outputted from the capacitor 134, and a capacitor 136 outputting the parabolic waveform voltage induced in a secondary side of the transformer (T) 132 through noise-removal and DC-coupling.
That is, the convex parabolic waveform voltage outputted from two ends of the basic S-regulation capacitor 119 is inverting-amplified through the capacitor 134 and the transformer (T) 132, and therefore changed into a convex parabolic waveform voltage to be outputted as the dynamic focus waveform voltage.
On the other hand, a monitor has various display modes. For example, a VGA mode has 640xc3x97480 resolution and a 31.5 KHz horizontal frequency, a SVGA mode has 1024*768 resolution and 35xcx9c37 KHz horizontal frequencies, and a high-resolution mode has 1024xc3x97768 through 1280xc3x971024 resolution and 64xcx9c75 KHz horizontal frequencies.
To oscillate a horizontal deflection signal corresponding to the horizontal frequency, the capacitance of the S-regulation circuit 120 should be altered, i.e., the higher the resolution is, the higher the frequency of horizontal deflection signal should be. However, the higher the frequency of horizontal deflection is, the lower the parabolic waveform voltage generated from the S-regulation capacitor 122 is.
As described above, a frequency inputted to a display apparatus is altered according to setting up a display mode of the display apparatus, and therefore a parabolic waveform voltage corresponding to the horizontal frequency is altered. Thus, it is impossible to generate a precise focus voltage.
Accordingly, the present invention has been made keeping in mind the above-described shortcomings and user""s need, and an object of the present invention is to provide a dynamic focus regulation circuit for supplying a uniform parabolic waveform voltage regardless of variation of a horizontal frequency in a display mode.
This and other objects of the present invention may be accomplished by the provision of a horizontal dynamic focus regulation circuit, which induces a horizontal dynamic focus waveform voltage by a horizontal deflection circuit generating a different frequency according to a display mode of a display apparatus, comprising a microcomputer outputting a plurality of control signals; a plurality of switching parts corresponding to the plurality of control signals outputted from the microcomputer, respectively; a plurality of S-regulation capacitors connecting with the plurality of switching parts in series, respectively; an auxiliary capacitor provided on a line diverged from a line connecting each switching part with each S-regulation capacitor, and being respectively connected with the S-regulation capacitor in parallel and series according to switching on and off of the switching part.
Preferably, each switching part is comprised of a transistor being switched on/off responsive to their respective control signals from the microcomputer according to the display mode.